At my first steps with Linux I was very familiar with KDE. The easy reason: it’s more Windows like. So I started at this time with SUSE 9.x and KDE 3.x, and it was just awesome!
Well, KDE 4 at the beginning was … let us say “a giant grizzling kid”. But since the latest versions it actually has grown up and I’ve tested it so many times so that I can say “Yes, it’s useable again!”. Anyway, I don’t want to roll back to KDE. Don’t get my wrong, I love Qt and C++ (for the development), but I actually don’t want to tune my desktop as much as I can, just to get a useable and good looking DE for me. People who just came from Windows and want to work on nearly the same way as they did under this OS, they can just go with KDE and I’m sure they will be happy. Also, people who want to configure every howsoever small thing at their DE are doing nothing wrong with useing KDE.
For myself, I have actually clear things, which I wanna do with my desktop. Compiling with GCC, bash access, the possibility to get onto my servers via SSH, surfing and checking my mails and at least, playing some games, but anyway the last point I have to do under Windows or my PS3 …
Over time of useing Linux and their DEs I found out, that I don’t need a high customizable desktop, I just need one who helps me to get my things done. Unity and even GNOME Shell are both desktops who gave me this possibility. And both aren’t that bad looking, which is a very nice side effect. Sure, you have to learn how to deal with some new features and ways to work but if you one time know, who to deal with this both new DEs, you will profit from it.
For example, even at the time I was useing KDE, I started to get programs running with the help of “ALT+F2” (KRunner). So, the SUPER key useage at Unity and GNOME Shell is the best way for me to start my programs.
Yes, I have to say, I like both desktops GNOME Shell and Unity. But if I would get forced to just pick one of those, I would go with GNOME Shell. But you know what, I’m useing Linux, so I didn’t get forced to anything 😉

I also looking sometimes to the GNOME Panel, better known as “GNOME Fallback”. For me it is also useable. It brings me the GNOME 2 feeling back and with the combination of ALT+Right click I’m also able to add new stuff to my panels. Well, I read always that there isn’t the whole stuff available for the GNOME 3 Panel, which was available for GNOME 2, but I personally just used the “Process Monitor” applet as additional stuff on GNOME 2, which is also available under GNOME 3 Panel.

That said, I’m actually useing some “hybrid modes” for myself. At work, I have an instance of Ubuntu 12.04 with GNOME Panel and an instance of openSUSE Tumbleweed with GNOME Shell running. I’m also thinking about to install GNOME Shell under Ubuntu, too.
At home my notebook is running Ubuntu with Unity and GNOME Panel. I like to use Unity when it comes to mobility and I like to use the classic GNOME Panel when it comes to “workstation replacement” (this means the notebook connected to a monitor for me).

Anyway, use what you want or better, use what’s fits best for you. You want have new (eventually smarter) ways to work and you don’t need a high customizable DE? Try GNOME Shell or Unity. You want the possibility to configure everything at your DE? Try KDE! You want a high customizable DE with lower consumption of RAM? Try Xfce.